The present invention is generally directed to thermal processing chambers for heating semiconductor wafers using light energy. More particularly, the present invention is directed to improved heating lamp configurations containing tuning devices which are used to more uniformly heat semiconductor wafers.
A thermal processing chamber as used herein refers to a device that rapidly heats objects, such as semiconductor wafers. Such devices typically include a substrate holder for holding a semiconductor wafer and a light source that emits light energy for heating the wafer. During heat treatment, the semiconductor wafers are heated under controlled conditions according to a preset temperature regime. For monitoring the temperature of the semiconductor wafer during heat treatment, thermal processing chambers also typically include temperature sensing devices, such as pyrometers, that sense the radiation being emitted by the semiconductor wafer at a selected band of wavelengths. By sensing the thermal radiation being emitted by the wafer, the temperature of the wafer can be calculated with reasonable accuracy.
In alternative embodiments, instead of or in addition to using radiation sensing devices, thermal processing chambers can also contain thermocouples for monitoring the temperature of the wafers. Thermocouples measure the temperature of objects by direct contact.
Many semiconductor heating processes require a wafer to be heated to high temperatures so that various chemical and physical reactions can take place as the wafer is fabricated into a device. During rapid thermal processing, which is one type of processing, semiconductor wafers are typically heated by an array of lights to temperatures, for instance, from about 400xc2x0 C. to about 1,200xc2x0 C., for times which are typically less than a few minutes. During these processes, one main goal is to heat the wafers as uniformly as possible.
Problems have been experienced in the past, however, in being able to maintain a constant temperature throughout the wafer and in being able to control the rate at which the wafer is heated. If the wafer is heated nonuniformly, various unwanted stresses can develop in the wafer. Not being able to heat the wafers uniformly also limits the ability to uniformly deposit films on the wafers, to uniformly etch the wafers, beside limiting the ability to perform various other chemical and physical processes on the wafers.
Temperature gradients can be created within the wafer due to various factors. For instance, due to the increased surface area to volume ratio, the edges of semiconductor wafers tend to have a cooling rate and a heating rate that are different than the center of the wafer. The energy absorption characteristics of wafers can also vary from location to location. Additionally, when gases are circulated in the chamber, the gases can create cooler areas on the wafer due to convection.
In the past, various lamp configurations have been proposed in order to overcome the above described deficiencies and improve the ability to heat wafers more uniformly and to control the temperature of the wafers at various locations. These systems, however, have become increasingly complex and expensive to produce. For instance, some systems can contain well over 100 lamps.
As such, a need currently exists for an improved thermal processing chamber that is capable of uniformly heating semiconductor wafers in a relatively simple manner without being as complex as many prior art systems. A need also exists for an improved rapid thermal processing chamber for heating semiconductor wafers that is equipped with controls for varying the amount of energy that is applied to the wafer at different locations based upon the characteristics and properties of the wafer. Such controls are especially necessary due to the increasing demands that are being placed upon the preciseness at which the semiconductor wafers are heat treated and at which semiconductor devices are fabricated.
The present invention recognizes and addresses the foregoing disadvantages and others of prior art constructions and methods.
Accordingly, it is an object of the present invention to provide an improved thermal processing chamber for heat treating semiconductor wafers.
Another object of the present invention is to provide a thermal processing chamber having an improved lamp configuration for heating the wafers uniformly.
Still another object of the present invention to provide a heating device for use in thermal processing chambers that contains a plurality of lamps which form overlapping heating zones on a wafer being heated.
Another object of the present invention is to provide a heating device for use in thermal processing chambers that contains tuning devices spaced between heating lamps for uniformly heating wafers with high levels of controllability.
It is another object of the present invention to provide a heating device for use in thermal processing chambers that not only contains lamps for heating semiconductor wafers but also contains a tuning device for heating the wafers more uniformly, wherein the tuning device comprises a lamp in operative association with or without a focusing lens which is used to direct light energy being emitted by the lamp onto a determined area of the semiconductor wafer.
Another object of the present invention is to provide a heating device for use in thermal processing chambers containing a plurality of lamps for heating a semiconductor wafer and at least one passive optical element placed amongst the lamps which redirects light energy being emitted by the lamps for heating semiconductor wafers more uniformly.
Still another object of the present invention is to provide a heating device for use in thermal processing chambers that contains passive optical elements having a ruled prismatic surface which is positioned within the heating device in order to redirect light energy being emitted by the heating device onto a semiconductor wafer in a manner that heats the wafer more uniformly.
These and other objects of the present invention are achieved by providing an apparatus for heat treating semiconductor wafers. The apparatus includes a thermal processing chamber adapted to contain a semiconductor wafer. For instance, a substrate holder can be contained within the chamber upon which the wafer is held. A heating device is placed in communication with the thermal processing chamber which emits thermal light energy onto the wafer held on the substrate holder. The heating device can include an assembly of light energy sources which are positioned, for instance, to heat different zones of the wafer. The light energy sources form an irradiance distribution across a surface of the wafer.
More particularly, during the heating process, either the semiconductor wafer can be rotated or the light energy sources can be rotated. In this manner, the light energy sources form radial heating zones on the wafer which aid in heating the wafer uniformly and provide good temporal control during the heating cycle.
In accordance with the present invention, the heating device further includes at least one tuning device positioned amongst the light energy sources. The tuning device is configured to change the irradiance distribution of the light energy sources in a manner for more uniformly heating the semiconductor wafer. The tuning device can be an active device which emits light radiation onto a determined location of the wafer or can be a passive device, which redirects light radiation being emitted by the light energy sources contained in the heating device for adjusting the irradiance distribution of the light energy sources.
In one example of an active device, the tuning device includes a light energy source spaced from one or more focusing lenses. The focusing lens is configured to focus light energy being emitted by the light energy source onto a determined location of the wafer. The light energy source and the focusing lens can be mounted to a movable support structure. The support structure can be movable for directing the light energy being emitted by the tuning device onto different locations as desired depending upon the particular application. In general, the tuning device is used to supply light energy to the wafer in areas where further heating is desired in order to compensate for any nonuniformities in the irradiance distribution of the plurality of light energy sources.
In one embodiment, the support structure to which the light energy source is mounted includes a tiltable lever arm. The lever arm is tiltable for directing light energy being emitted by the tuning device to a particular location.
The system of the present invention can include as many tuning devices as are required for uniformly heating wafers. The number of tuning devices incorporated into a particularly system will generally depend upon numerous factors, including the configuration of the light energy sources. In one embodiment, the light energy sources can be placed in concentric rings and tuning devices can be placed in between the rings of lamps.
In order to control the amount of light energy that is emitted by the plurality of light energy sources, the apparatus of the present invention can include at least one temperature sensing device which senses the temperature of the wafer at a plurality of locations. For instance, the temperature sensing device can be a plurality of pyrometers, one pyrometer with multiple viewing ports, or one or more thermocouples. The temperature sensing devices can be in communication with a controller, such as a microprocessor, which determines the temperature of the wafer. The controller, in turn, can be in communication with the power supply of the light energy sources for controlling the amount of heat being emitted by the light energy sources in response to the temperature of the wafer. The controller can be configured, for instance, to control the amount of light energy being emitted by each light energy source or can control different groups of the light energy sources.
In one embodiment, the controller can be configured to also control the amount of light energy that is being emitted by a tuning device installed in accordance with the present invention. In particular, the controller can be used to control the tuning device independent of the light energy sources. Further, the controller can also be configured to be capable of automatically moving the support structure upon which the tuning device is mounted in order to change and adjust the location of where the light energy being emitted by the tuning device contacts the wafer.
The light energy sources used in the heating device of the present invention can be, for instance, lamps, such as tungsten-halogen lamps. The lamps can be substantially vertically oriented with respect to the semiconductor wafer (see FIG. 2), or can be oriented horizontally (see FIG. 1). In order to maintain the lamps in position, the lamps can be connected to a mounting base. The mounting base can include reflective devices for directing the light energy being emitted by the lamps onto the wafer. The reflective devices can be polished annular surfaces surrounding the lamps or, alternatively, can be in the shape of plates that extend adjacent to the lamps. For example, in one embodiment, the heating device includes reflective plates which extend beyond the length of the lamps in a direction perpendicular to the semiconductor wafer.
Besides using active tuning devices that emit light radiation, the present invention is also directed to the use of passive tuning devices which redirect light energy being emitted by the light energy sources. In particular, the light energy is redirected in a manner such that semiconductor wafers are heated more uniformly. In this embodiment, the tuning device can comprise an optical element positioned adjacent to at least one of the light energy sources. The optical element can be designed either to reflect, to absorb, or to refract light energy.
In one embodiment, the optical elements can include a ruled prismatic surface for reflecting light radiation in a specified manner. The ruled prismatic surface can have a fixed pitch and a fixed facet angle or a fixed pitch with a variable facet angle. The ruled prismatic surface can be made from a highly reflective material, such as a dielectric material or a metal, such as gold.
Besides having a ruled prismatic surface, in an alternative embodiment, the optical element can include a diffuse surface, which scatters light energy in all directions. The diffuse surface can be made from, for instance, a rough surface.
Preferably, the passive tuning device has an adjustable position with respect to the light energy sources contained in the heating device. For instance, in one embodiment, the tuning device can be placed at different angles with respect to the light energy sources and at a different height. For instance, the light energy sources can be all attached to a mounting base and can all be substantially vertically oriented. The tuning device can be designed to be insertable in and out of the mounting base so as to be positioned at a different height with respect to the light energy sources. The position of the tuning device can be controlled using a controller if desired.
Other objects, features and aspects of the present invention are discussed in greater detail below.